1. Field of the Invention.
The present invention relates to a masterbatch and more particularly, to a free-flowing, powdery masterbatch including a metal oxide, having a material that is absorbed within the intra-aggregate void space of the metal oxide, and a resin system incorporating same.
2. Background of Related Art
Adhesive and sealants are widely used throughout the world in many commercial and industrial applications ranging from textiles and shoes to automotive and aerospace. In general, an adhesive composition is used to bind two substrates together, while a sealant composition is generally used to form a load-bearing elastic joint between two substrates. While there are a wide variety of end item applications for sealants and adhesives, their fundamental purpose is the same, i.e. to adhere to or bind substrates. As a result, there is a fair degree of overlap in the function of adhesive and sealant compositions. A useful adhesive or sealant should exhibit certain performance characteristics, including for example, good flow and handling characteristics, good sag resistant, and good shelf life.
Many adhesives and sealants are derived from a family of materials commonly know as resins. A resin can be a naturally occurring product such as copal, rosin, balsam, or amber, or can be a synthetic product such as a urethane, acrylic, glycol, epoxy, polyester or a polyol. Epoxy resins are commonly used structural adhesives and sealants because of their strength, versatility, and excellent adhesion to a variety of surfaces. Generally, epoxy resin systems are formulated into either one or two-component, ambient or heat-cured paste or films. Typical ingredients added to the epoxy resin systems, depending on the desired end product formulation, include curing agents, catalysts and accelerators, fillers, pigments, reactive diluents, non-reactive diluents, solvents, flexibilizers, and rheology control agents.
Good rheological control is important in resin systems, such as, epoxy resin adhesives and sealants, to allow thinning under shear for easy application and wetting of surfaces while retaining good sag resistance properties, and a uniform dispersion of the formulation ingredients. Common rheological control agents for use in resin systems include, among others, calcium carbonates, clays, cellulosic and natural gums, pulp fibers, and metal oxides, including, alumina, and silica. For example see U.S. Pat. Nos. 4,695,605, 4,320,047, and 4,728,384, the specifications of which are incorporated in their entirety by reference.
Fumed silica is a popular rheology control agent for use in resin based adhesives and sealants. See, for example, Cabot Corporation Technical Data pamphlets entitled "Cab-O-Sil TS-720 Hydrophobic Fumed Silica," and "Cab-O-Sil Funed Silica in Adhesives and Sealants." The use of a fumed silica usually requires more than 5 weight percent of the fumed silica to achieve good rheological control. However, such high concentrations of fumed silica can have detrimental effects on system viscosity.
The mixing of rheology control agents into adhesives or sealants is a known process often resulting in enhanced material properties of the adhesive or sealant itself. However, the incorporation of rheology control agents, for example metal oxides, into an adhesive or sealant is often difficult as many adhesives and sealants are highly viscous materials, and the metal oxides themselves are often a dry, dust like material making many conventional materials handling methods impractical. Because of the characteristics of the products, incorporation often results in incomplete and non-uniform dispersion of the rheology control agent into the adhesive or sealant. To remedy this problem, it has been suggested to prepare a pre-mix of a rheology control agent and a carrier material to form a wet masterbatch material and then incorporate the wet masterbatch into the desired system to form an adhesive or sealant.
A wet masterbatch material may be prepared by starting with a carrier adhesive or sealant material, for example a resin, and adding to that resin a rheology control agent, for example a fumed silica. The fumed silica is generally added in an amount less then about 23% by weight of fumed silica. A wet masterbatch whose composition exceeds 23% by weight of fumed silica often results in an agglomerated material that does not fully disperse when mixed with a base material, such as a resin. See for example, Sweeney, "Fumed Silica's Growing Role in Non-Sag Sealants and Adhesives," Adhesive Age, pp 32-34, (January 1967).
While the use of a wet masterbatch is an improvement over the direct mixing of the fumed silica into a base resin, the wet masterbatch is not without disadvantages including, for example, the difficulties and costs associated with the handling and transfer of the wet masterbatch materials. Since a wet masterbatch is primarily resin, it is a viscous, pasty, and sticky material which makes common handling methods for such material impractical. As a result, more costly methods of handling wet materials must be employed. In addition to the problems associated with handling of the wet masterbatch is the loss of material from adhesion to containment vessels and transfer devices and the costs associated the with cleaning and removal of the residual material from such containers and transfer devices. Accordingly, a need remains for rheology control agents with improved handling characteristics, ease of incorporation and processability.
In addition, a further need remains for improved rheology control agents that will permit a more complete dispersion into adhesive or sealant materials, and in particular a method that would permit a more complete dispersion of a metal oxide rheology control agent into base resin.